1. Field of the Invention
The present invention relates to a high frequency semiconductor device having an improved package structure.
2. Description of Related Art
In the prior art, a typical one of package structures for a semiconductor device has been constituted of a first level square ceramic substrate having a die attaching area formed by printing a tungsten paste on a central portion of the substrate. A second level ceramic substrate in the form of a square ring is laminated on an upper surface of the first level ceramic substrate in such a manner in that the die attaching area is exposed and surrounded by the second level square ring substrate. In addition, a number of radial-patterned conductors composed of a tungsten paste are printed on an upper surface of the second level square ring substrate. A third level ceramic substrate in the form of a square ring, which has an inner size larger than that of the second level square ring substrate but an outer size smaller than that of the second level square ring substrate, is laminated on the second level square ring substrate for the purpose of insulating and protecting the radial conductors, in such a manner that respective inner tip ends of the radial conductors positioned in a periphery of the die attaching area are exposed. In addition, a seal frame for supporting a cap is mounted on the third level square ring substrate, and patterned side metallized conductors are provided on a side surface of the laminated substrates.
Thereafter, the substrates thus prepared are sintered in an oxidizing atmosphere of 1500.degree. C. to 1600.degree. C., so that the tungsten paste reacts with the ceramic so as to be metallized. The metallized conductors are plated with Ni and Au, respectively. Thus, a semiconductor device package is completed.
On the die attaching area of the package thus formed, a semiconductor device chip is bonded by use of an Au--Si solder, and pads of the die-bonded chip are connected to corresponding radial-patterned conductors by means of aluminum wires. In addition, external lead wires are connected to corresponding patterned side metallized conductors, respectively.
In the above mentioned package structure, the substrates constituting the package and other materials has a large dielectric constant, and a spacing between adjacent metallized patterned conductors is narrow. Therefore, an electrostatic capacitance between adjacent lead conductors is large, and isolation between the lead conductors and gain is not satisfactory. In addition, a resonance frequency of the semiconductor device is low. As a result, the above mentioned package structure has been difficult to use as a high frequency semiconductor device package.